Primary lymphocytes, both human and animal, are difficult to maintain in continuous culture. Short term cultures of B-lymphocytes can be maintained long enough to produce limited amounts of specific antibody. Generally, it is necessary to repeatedly stimulate primary, antigen-specific lymphocytes with antigen in media containing expensive lymphokines. Failure to include such lymphokines, either exogenously or by autologous monocytes, often results in cell death. Attempts to produce continuous mouse lymphocyte cell lines by infection of stimulated cells with viruses such as Abelson virus produce only cell lines with pre-B-cell characteristics. Infection of human B-lymphocytes with Epstein Barr virus has had limited success. Such cell lines, however, usually make limited amounts of antibody for a period of only a few weeks.
The advent of hybridoma technology provided a method of producing lymphocyte cell lines that are continuous (i.e., maintainable in culture indefinitely without added lymphokines) and stable (i.e., maintaining antigen-specific immunological function such as antibody production). Basically, the procedure involves the fusion of two somatic cell; a cancerous B lymphocyte (myeloma) and a normal, stimulated B lymphocyte that produces the desired antibody. Although hybridoma technology has revolutionized immunology, the procedure is limited by the availability of plasmacytoma cell lines suitable for hybridoma production. In addition, fusion efficiency (i.e., the relative number of hybridomas with a desired function recovered from the fusion media) is low, particularly for fusions between human lymphocytes.
Certain cell lines have been susceptible to transformation with exogenous DNA. Mouse fibroblast cells have previously been transformed by transfection with oncogenic DNA. See Weinberg, (1981) Biochem. Biophys. Acta 651: 24-35; Krontiris et al., (1981) Proc. Natl. Acad. Sci. USA 78: 1181-1184; Shih et al., (1981) Nature (London) 290: 261-164; Perucho et al., (1981) Cell 27: 467-476. Hamster fibroblast cells have also been transformed by transfection with oncogenes. See Smith et al., (1982) Proc. Natl. Acad. Sci. USA 79: 1964-1968. Other cells, such as mouse bone marrow cells and fibroblast cells have been transfected by non-oncogenic DNA, such as the thymidine kinase gene from the herpes simplex virus. See Cline et al., (1980) Nature (London) 284: 422-425; Mercola et al., (1980) Science 208: 1033-1035; Pellicer et al., (1980) Science 209: 1414-1422. Very few cell types, however, have been identified that are susceptible to transfection with exogenous DNA.